The goals of this laboratory are to analyze the development and differentiation of B lymphocytes, and to examine some of the regulatory mechanisms involved in lymphocyte interaction. Emphasis is placed on examing to antigens which are under immune response (Ir) gene control, since these genes regulate the ability of animals to respond to antigen immunization. Studies using mice expressing the CBA/N sex-linked immune defect (xid) indicate that in addition to responding poorly to T cell independent antigens, such mice manifest poor antibody responses to certain T cell dependent antigens such as PGAL, TGAL, and DNP-TGAL (all under Ir gene control). Analysis of the surface immunoglobulin capping parameters of mice expressing the CBA/N defect indicate that their B cell population is adult-like, even though by other criteria their B cell population is characteristic of early (neonatal) developing B cells.